Researchers Find 100-Million-Year-Old Virus In The Blood Of Pregnant Women

It's part of our genome today  and we're not sure what it does, exactly. Natali_Mis/Shutterstock

Did you know that you have ancient viruses in your genome? This isn’t so surprising when you think about it – your genetic blueprint is comprised of DNA fingerprints from all walks of life. A virus, though, is perhaps a more jarring thought, and as a new spotlight on the subject has revealed, scientists have recently identified yet another infiltrator concealed within us.

As reported in the journal Trends in Microbiology, a virus that first infected our ancestors 100 million years ago – during the heyday time of the dinosaurs – stayed with us, all throughout the extinction of the reptilian beasts and the evolution of primates. Today, it’s a human gene that is expressed in embryos and cancers. It can even be found in the blood of pregnant women.

These genomic invaders are known as human endogenous retroviruses, or HERVs. Importantly, they no longer behave as viruses, in that their genetic material – RNA, a “cousin” to DNA – has been subsumed within our genome. This now gets passed down to our children, if we choose to have them.

Sometimes, researchers find fragments of viral DNA within our genome, but on occasion, entire sequences are discovered.

These ancient viruses all appear to be retroviruses. They infect their host cells by inserting a DNA replica of their RNA into the genome. Normally this causes a problem – as the human immunodeficiency virus does today – but it appears that sometimes the infection can be innocuous, at least during the viral infection stage.

This new viral remnant means that, by the latest estimate, 8 percent of our entire genomes are comprised of ancient viruses. Tantalizingly, we have no definitive idea of what they do.

“What do these efficient genomic colonizers do?” the paper’s authors wondered. “Are they merely fossils that, like mosquitos in amber, were stuck and preserved in large host genomes while their functions decayed?”

The team, led by the National and Kapodistrian University of Athens, explained that “researchers have been struggling to understand their roles for as long as we have known them, postulating junk, bystander, and pathogen hypotheses.”

Referencing another research group, the team’s article elucidates on how this 100-million-year-old HERV was discovered mid-transferal from the fetus to the mother’s bloodstream during pregnancy. Although the gene appears to be fairly inactive at most stages, it seems to be expressed far more when it’s in the placenta and in cancerous tissues, particularly ovarian cancer.

This implies that it’s involved in the “manipulation of stem cells and early life events, which could have very important effects on adult diseases,” including cancer, but we can’t yet be certain. It’s a discovery that’s simply raised more questions than it’s answered.

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